While DDG uses a myriad of data sources, it's main search functionality is powered by Yahoo BOSS API. They should easily be able to switch over to BING API as Yahoo BOSS has delivered 100% Bing results anyway. However, the ads that DDG shows, and therefore their whole business model, are also powered by Yahoo BOSS API. So they will be able to continue their search engine but they won't make any money from it unless they cut a new deal for search ads.